This invention relates to a knitting tool, for example, a selector sinker or a needle for a knitting machine and is of the type which has a flat shank and further has an elongated, narrow control spring which projects from the shank in the region of a narrow side thereof and which is secured to the shank at one spring end.
German Offenlegungsschrift (application published without examination) 15 85 211 describes a circular knitting machine having an electronic needle selecting system in which the needles are controlled by plungers formed as selector sinkers which, according to the knit pattern, may be pivoted radially back and forth between an operative and an idle position to cause them to engage or disengage a cam track. Each selector sinker carries in the region of its narrow side a projecting control spring formed as a small spring bar which, at one end, is anchored in a shank portion of the selector sinker. The control spring, in the region of its free end, engages a countersupport on the needle cylinder and functions as a resetting spring for the electromagnetically controlled selector sinkers.
For anchoring the control spring in the shank part of the selector sinker, one end portion of the control spring is bent to have two legs arranged as a hairpin, and one leg is pressed into an outwardly flaring, slot-like aperture of the shank portion. Since, with such a securement, the control spring is merely clamped with its end portion into the slot-like recess of the shank part of the selector sinker and thus is only frictionally held under bias, there is a risk that in the course of an extended service, because of the high dynamic loads on the control spring, its end portion slightly creeps outwardly of the slot-like recess of the shank part of the selector sinker. As a result, undesired friction forces are generated in the associated guide channel for the needle and the selector sinker in the needle cylinder. Furthermore, uncontrolled dimensional changes in the position of the control springs with respect to the selector sinkers may appear which also adversely affect the operation of the knitting machine.
Basically the same considerations apply to another known selector sinker disclosed in U.S. Pat. No. 3,643,472. The selector sinker illustrated in FIG. 10 of that patent has a control spring whose end portion is clamped into a recess having parallel sides extending approximately at right angles to the longitudinal axis of the sinker. The control spring is secured against axial movements by a rectangularly bent end part. For this purpose the sinker must be provided with an essentially L-shaped, slot-like recess which involves manufacturing difficulties.
Further, German Offenlegungsschrift 23 27 585 describes a circular knitting machine operating with needles which carry, at their shank part, a unilaterally anchored control spring serving the magnetic needle selecting system. In this arrangement the control spring is, with its end portion, fitted into a parallel-sided slot in the needle shank portion and is immobilized therein by wedging. The control spring is made of a thin spring steel plate or of a cross-sectionally round or slightly flat-rolled spring steel member to exhibit flattened portions. While a form-fitting connection between the end of the control spring and the needle shank portion may be obtained, the individual, spaced embossed locations in the region of the side walls of the slot do not ensure an accurate, lateral orientation of the control spring relative to the needle shank. Since the control spring is of a hard material and therefore is not deformed during upsetting (wedging), risks prevail that due to the earlier-mentioned high dynamic loads imparted on the control spring, its end portion frees itself slightly from the upset parts after a certain period of time. As an undesired result, the entire control spring could rotate--to a limited extent--in the anchoring slot. It is a further risk that the slot is widened by the transverse forces which are generated during the upsetting (wedging) operation and thus the height dimension of the shank changes in an uncontrollable manner.
A significant improvement of the anchoring of the control spring in the shank of a knitting tool, such as a selector sinker or a needle for a knitting machine is achieved by the construction described in U.S. Pat. No. 5,076,074. In the shank portion of the knitting tool described therein a depression is provided which adjoins a slot-like aperture open towards the narrow side of the shank. The width of the depression, measured transversely to the longitudinal dimension of the aperture, is at least at some locations greater than the width of the aperture. The control spring has at its end portion an anchoring section which is enlarged corresponding to the width of the depression and whose thickness is less than or is equal to the depth of the depression. The control spring is at least on one side laterally guided in the aperture and is fitted into the depression with its anchoring section. The position of the aperture and the depression define an exact orientation of the control spring in a respective predetermined position thereof, and the enlarged anchoring section prevents an undesired turning of the control spring. The depression ensures an unequivocal firm association of the control spring with the shank portion of the knitting tool, providing for a possibility of a very accurate, positionally correct installation of the control spring.
All of the above-described knitting tools are of a two-part construction; that is, the knitting tool proper on the one hand and the control spring, on the other hand, are manufactured as separate parts and are subsequently form-fittingly secured to one another and, if required, additionally immobilized. Such a two-part configuration of the knitting tool is relatively expensive. Furthermore, the recess or the depression in which the control spring is anchored is, as viewed transversely to the longitudinal dimension of the needle shank, necessarily spaced from the narrow side of the shank in the vicinity of the control spring to ensure that in the region of the recess or depression sufficient shank material remains for a secure anchoring of the inserted part of the control spring.
Recently sinkers have been developed which, together with their control spring, are made of a single piece and are hardened and ground. Corresponding to the earlier-noted two-part selector sinkers, in the single-piece construction the end portion of the control spring formed at the shank and connecting the control spring with the shank is, as viewed transversely to the longitudinal direction of the shank, at a significant distance from the narrow shank side associated with the control spring, at a location which corresponds approximately to the mid height of the shank. Between the control spring and the shaft region at the narrow shaft side facing the control spring, a narrow, slot-like space is provided which opens towards the free end of the control spring. The slot-like space permits the control spring the free mobility required for performing its function during operation. Also, a further slot-like space is provided which opens towards the oppositely situated narrow side of the shank in the zone of the end portion of the control spring formed on the shank. Such a further slot-like space is shorter in the longitudinal shank direction and is bounded by an upstanding finger or a pin-like extension. Such a rigid attachment serves as a support location on which lies the selector sinker inserted into a guide channel of the knitting machine and which contains the axis about which the selector sinker pivots under the effect of the associated cams during operation.
A selector sinker of the above-outlined structure involves the risk that after a longer service period during which high dynamic loads are generated, the control spring may break due to material fatigue, particularly in the region of its end portion formed on the shank.